Nicolas Sarkozy addresses a press conference at the close of an extraordinary meeting of eurozone leaders in Brussels called to discuss the implications of Greece's financial crisis Photograph: Michel Euler/AP

EU leaders have agreed a financial defence plan in an attempt to protect the eurozone countries from speculative attacks in the wake of the Greek debt crisis.

The German chancellor, Angela Merkel, and the French president, Nicolas Sarkozy, said today that an "intervention unit" designed to preserve financial stability in the 16 eurozone countries would be in place by Monday when the markets reopen.

The creation of the unit, which will have up to €70bn at its disposal to shield the euro against further market speculation, comes after the shared currency's value fell amid fears that member countries such as Spain and Portugal could suffer similar debt problems to Greece.

Today's announcement follows an agreement yesterday by the eurozone leaders for a €110bn (£95bn) EU-International Monetary Fund rescue package for Greece to prevent its debt crisis from spreading.

Announcing the stability plan Sarkozy said: "The euro is an essential element of Europe. We cannot leave it to speculators. We will not let others undo what generations have created."

Merkel said the mechanism would send a "very clear signal" to market speculators to back off.

The German chancellor had earlier spoken to the US president, Barack Obama, who called for a "strong policy response" involving the wider international community.

The finance ministers of all 27 EU member states will hold another emergency meeting tomorrow to draw up further detail of the anti-speculation plan, which will also include the European Central Bank.

The summit in Brussels, originally called to sign off the Greek bailout plan, turned into one of crisis management amid market turmoil.

It comes as Spain and Portugal begin to suffer similar financial problems to Greece, with borrowing costs increasing and talk of speculative attacks.

Despite reassurances from EU leaders that the Greek debt crisis is a unique combination of bad management, overspending and statistical cheating, markets have continued to sell off the euro, leading it to fall to its lowest value against the dollar in more than a year.

Several leaders, including Sarkozy and Merkel, want a fundamental revamp of the rules for managing the euro.

"We must sharpen the edge" of the rules to keep wayward governments in line and consider revising the 1992 treaty that laid the groundwork for the shared currency, Reuters reported Merkel as saying.

The European commission president, José Manuel Barroso, said: "We will defend the euro whatever it takes. We have several instruments at our disposal and we will use them."

Jean-Claude Juncker, who heads the Eurogroup of eurozone finance ministers, said: "We are talking about a global attack against the euro, and the eurozone must react as one."